15 - Type Ia supernovae: spectroscopic surprises

Summary

Abstract

Recent observations have extended the range of diversity among spectra of Type Ia supernovae. I briefly discuss SN Ia explosion models in the spectroscopic context, the observed diversity, and some recent results obtained with the Synow code for one normal and two peculiar SNe Ia. Relating the observational manifestations of diversity to their physical causes is looking like an ever more challenging problem.

Introduction

“Surprises” refers not only to some recent developments in Type Ia supernova (SN Ia) spectroscopy that will be discussed below, but also to additional recent discoveries that I will be able only to mention, such as the polarization signal in SN 2001el (Wang et al. 2003; see also the chapter by Wang); the unusual properties of SN 2001ay (see the chapter by Howell); and the circumstellar Hα emission of SN 2002ic (Hamuy et al. 2003; see also the chapter by Hamuy). The scope of this chapter is restricted to photospheric—phase optical spectra. For recent results on infrared spectra see, e.g., Marion et al. (2003).

Some background, including mention of the various kinds of SN Ia explosion models in the spectroscopic context, is in §15.2. An overview and update of the SN Ia spectroscopic diversity is in §15.3. Some recent results from direct analysis of the spectra of three events (the normal SN 1998aq and the peculiar SNe 2000cx and 2002cx), obtained with the parameterized, resonance scattering code Synow, are discussed in §15.4. The final section (§15.5) contains more questions than conclusions.